Flashing light device with automatic daytime shutoff



April 21, 1964 H. R. MALLORY 3,130,349

FLASHING LIGHT DEVICE WITH AUTOMATIC DAYTIME SHUTOFF' Filed Dec. 22. 1960 INV EN TOR. AA/RF A. 464.410

United States Patent f 3,13%,349 FLASHING LEGHT DEWCE WITH AUTGMATHJ DAYlll /fi SHUTGFF Henry R. Mallory, Greenwich, Conn, assignor to P. R. Mallory & Co., inc, Indianapolis, Ind, a

corporation of Delaware Filed Dec. 22, 1960, Ser. No. 77,560 6 Claims. (Cl. 315-151) This invention pertains to flashing light devices suitable for use as warning markers or dipslays at nighttime, and is particularly directed to a flashing light device which shuts off automatically at the onset of daylight.

An important aspect of modern highway safety practice resides in the use of portable battery-operated flashing light devices to clearly demarlr the presence of barricades and other hazards at nighttime. For such application these devices must be economical in construction and operation as well as completely reliable. The total current drain on the battery during each twenty-four hour daily period is therefore highly important, a low value thereof leading to increased battery life and consequent increased reliability. By utilizing transistors in lieu of relays or vacuum tubes it has been possible to reduce the current consumed during flash operation to relatively low levels. However, a saving of about half of the total daily current drain could be achieved if the device auto matically turned itself off at the onset of daylight. Unfortunately, prior attempts to provide automatic daylight shutoff have required considerable additional circuitry including extra transistors and very often relays as well. This feature has therefore been regarded as too troublesome and expensive to be included in any flashing light device intended to find real commercial acceptance.

A further obvious application of a flashing light device having an automatic daylight shutoff feature is to advertising displays and signs. Flash operation at nighttime will obtain attention more effectively than a continuous light, and the daylight shutoff feature will enable use in unattended locations. Of course, even where an electric power line outlet is available, so that conse vation of current is of minor importance, this feature will dispense with the need for auxiliary equipment or an attendant to switch the display on and off each day.

Accordingly, an object of the invention is to provide a compact and efficient flashing light device which automatically shuts itself ofl? when the ambient light reaches a selected intensity level.

A further object is to provide a flashing light device wherein automatic daytime shutofi is an integral feature of the mechanism by which flash operation is produced at nighttime.

A further object is to provide a flashing light device wherein automatic daytime shutoff is obtained without requiring auxiliary circuitry or significant additional current drain from the power source.

Briefly, one embodiment of a flashing light device in accordance with the invention comprises a current supply circuit with a transistor and a lamp connected in series therein so as to cause the lamp to turn on at full intensity when the transistor is fully conductive and cause the lamp to turn off when the transistor is nonconductive. The device also comprises photosensitive means disposed in proximity to the lamp so as to be subjected to the light therefrom as well as to the ambient light in the vicinity of the device, such photosensitive means having an electrical characteristic which varies in accordance with variations in the intensity of the light incident thereon. The device additionally comprises control means connected to the current supply circuit by the photosens tive means and which in responsive to variation of the A 3,130,349 Patented Apr. 21, 1964 ice latters electrical characteristic to produce a control voltage which ranges between a limiting level and a cutoff level in accordance with variation of the incident light between respectively corresponding threshold and selected high intensities, the selected hight intensity being at most equal to the full intensity of the lamp. Means are pro vided for further connecting the foregoing control means to the transistor so as to form a degenerative feedback loop wherein the control voltage causes the transistor to conduct to a degree ranging from fully conductive to nonconductive in correspondence with variation of the control voltage between its limiting and cutoff levels. Finally, means are provided for additionally connecting the control means to the transistor in a regenerative feedback loop which renders the transistor fully conductive for a controlled interval whenever the control voltage changes from the cutoff level toward the limiting level and which renders it fully monoconductive for a controlled interval whenever the control voltage changes from the limiting level toward the cutoff level. The lamp is thereby caused to cyclically flash fully on and off so long as the ambient light remains below the selected high intensity and is maintained off when the ambient light is at least at that intensity.

A more detailed description of the invention is presented in the following specification and accompanying circuit drawing, but it should be noted that the true scope of the invention is actually pointed out in the ensuing claims.

In a particular embodiment of a flashing light device in accordance with the invention as shown in the circuit drawing, it comprises a lamp 1 and a current supply circuit from a DC. source such as a battery 3. The supply circuit may simply be a pair of conductors 5 and 7 respectively connected to the negative and positive terminals of such D.C. source. A transistor 9 is connected in series with lamp 1 in the foregoing supply circuit so as to cause it to turn on at full intensity when the transistor is fully conductive and to cause the lamp to turn off when the transistor is nonconductive. Specifically, the emitter and collector of transistor 9 are connected in series with lamp 1 in the current supply circuit. Although either a PNP or NPN transistor may be employed, transistor 9 has been illustrated as type PNP. Accordingly, its emitter is connected to positive supply conductor '7 and its collector is connected via the filament of lamp 1 to the negative supply conductor 5. Photosensitive means such as a photocell 11, preferably of the solid state photoresistive type such as cadmium sulfide or cadmium selenide, is provided disposed in proximity to lamp 1 so as to be subjected to the light therefrom as well as to the ambient light in the vicinity of the complete device. The photosensitive means employed must have an electrical characteristic which varies in accordance with variations in the intensity of the light incident thereon. Specifically, in the case of photocell 11 its electrical resistance decreases as the intensity of the light incident thereon increases.

The complete flashing light device additionally comprises control means connected to the described current supply circuit by the photosensitive means and responsive to the variable electrical characteristic thereof to produce a control voltage which ranges between a limiting level and a cutoff level in accordance with variation of the incident light between respectively corresponding threshold and selected high intensities, the selected high intensity being at most equal to the full intensity of lamp 1. Assuming that the photosensitive means employed is photocell 11, as described, the control voltage will reach its limiting level at a high value of the photocell resistance and will reach its cutoif level at a low Value thereof. The high and low resistances referred to will respectively correspond to incident light of the foregoing threshold and selected high intensities on photocell 11. More specifically, the control means may include a second transistor 13 also of the PNP type connected to the battery supply circuit by photocell 11 and responsive to the resistance variation thereof to produce the aforementioned control voltage. To this end the control means may also include a resistor 15 connected in series with photocell 11 between the base of transistor 13 and negative supply conductor 5 so as to provide a base bias responsive to the resistance variation of the photocell. The control means may further include a resistor 17 for connecting the collector of transistor 13 to negative supply conductor 5, the emitter of transistor 13 being connected to the emitter of transistor 9. The resistance of resistor 15 should be high enough so together with the resistance of photocell 11 the total resistance connected to the base of transistor 13 is suflicient to bias it in the nonconductive state when the light incident on the photocell reaches some low threshold intensity. Subject to that limitation, the resistance of resistor 15 should be such that when the incident light on photocell 11 reaches a selected high intensity at most equal to the full intensity of lamp 1 the total resistance connected to the base of transistor 13 will become low enough to bias it in the fully conductive state. Transistor 13 will therefore produce a voltage at its collector which is most negative when the transistor is nonconductive and which is nearly at the po tential of positive supply conductor 7 when the transistor is fully conductive. This voltage is the control voltage referred to above, the limiting and cutolf levels thereof respectively corresponding to the nonconductive and fully conductive states of transistor 13. Those levels therefore also respectively correspond to the threshold and selected high intensity levels of the incident light on photocell 11.

The complete flashing light circuit also comprises means for connecting the described control means to transistor 9 so as to form a degenerative feedback loop wherein the control voltage produced by the control means causes that transistor to conduct to a degree ranging from fully conductive to nonconductive in correspondence with variation of the control voltage between its limiting and cutoff levels. More particularly, such a feedback loop may be established by simply providing a conductor 19 between the selector of transistor 13 and the base of transistor 9. Conductor 19 will also serve to establish resistor 17 as the base bias resistor for transistor 9. The net bias voltage so applied to the base of transistor 9 will be the control voltage produced at the collector of transistor 13. Plainly, when that voltage is at its limiting level and transistor 13 is nonconductive transistor 9 will be strongly forward biased and will therefore be fully conductive. Lamp 1 is thus lighted at full intensity. On the other hand, when the control voltage reaches its cutoff level and transistor 13 is fully conductive transistor 9 will be back-biased by the voltage drop across resistor 17 and so will be nonconductive. Lamp 1 will therefore be turned off. I In operation, whenever the ambient light incident on photocell 11 reaches the selected high intensity at which transistor 13 becomes biased fully conductive the control bias voltage applied to the base of transistor 9 will render it nonconductive. Since lamp 1 will then turn off, the circuit as described up to this point provides very effective automatic daylight shutoff.

When the ambient light intensity is very low, as at nighttime, transistor 13 will tend to become biased nonconductive. If that occurred transistor 9 would become biased fully conductive and lamp 1 would turn on at full intensity, immediately causing photocell 11 to reduce the total base bias resistance of transistor 13 so as to render it conductive. It is therefore clear that the circuit as described up to this point would inevitably operate in an intermediate condition wherein transistors 9 and 13 would each be partially conductive and lamp 1 would be partially on during the nighttime.

In order to preclude the foregoing situation and obtain strong flash operation at nighttime, applicants device further comprises means for connecting the described control means to transistor 9 in a regenerative feedback loop which renders it fully conductive for a controlled interval whenever the control voltage applied thereto changes from the cutoif level toward the limiting level and which renders it nonconductive for a controlled interval whenever the control voltage changes from the limiting level toward the cutoff level. Specifically, such means serves to connect transistor 13 to transistor 9 so as to render the latter fully conductive for a controlled interval whenever transistor 13 begins to change from the nonconductive to the conductive state and which renders transistor 9 fully nonconductive for a controlled interval whenever transistor 13 begins to change from the fully conductive toward the nonconductive state. Suitable connecting means for this purpose may take the form of a capacitor 21 and resistor 23 connected in series between the collector of transistor 9 and the base of transistor 13 by way of resistor 15. That is, resistor 23 is connected to the terminal 25 of resistor 15 opposite the terminal thereof directly connected to the base of transistor 13.

Assuming an ambient light below the selected high intensity level at which transistor 13 is biased fully conductive and maintains transistor 9 in the cutoff state, suppose first that transistor 13 has been fully conductive, that transistor 9 has been nonconductive, and that transistor 13 has begun to become less conductive. This will cause transistor 9 to begin to conduct to some slight degree, resulting in a voltage swing in the positive direction at its collector. This positive pulse is translated via capacitor 21 and resistors 23 and 15 to the base of transistor 13, accentuating the tendency of that transistor to become less conductive and so producing a negative pulse at its collector. Via conductor 19 this pulse is conveyed to the base of transistor 9 where it tends to render that transistor still more conductive. A regenerative feedback operation thus occurs which almost instantly drives transistor 9 to the fully conductive state and transistor 13 to the nonconductive state. Lamp 1 is, correspondingly, almost instantly caused to light at full intensity and lowers the resistance of photocell 11 to a point at which transistor 13 becomes biased so as to normally be fully conductive. However, transistor 13 is prevented from conducting for a selected interval because of the capacitive charging current which flows from the collector of transistor 9 through capacitor 21, resistor 23 and photocell 11. This current maintains the voltage at terminal 25 of base bias resistor 15 sufliciently positive to maintain transistor 13 nonconductive for an interval dependent on the time con stant of the foregoing charging path. During the charging interval the voltage at terminal 25 will exponentially drop toward the quiescent bias level set by resistor 15 and the low resistance of photocell l1, finally reaching a point determined by the resistance of resistor 15 at which transistor 13 can begin to conduct. A positive-going pulse is then produced at its collector and is conveyed via conductor 19 to the base of transistor 9, causing it to become less conductive. The resulting negative-going pulse at the collector of transistor 9 is fed back through capacitor 21, resistor 23 and resistor 15 to the base of transistor 13, and a reverse regenerative operation takes place which almost instantly drives transistor 9 to the nonconductive state and transistor 15 to the fully conductive state. Of course, this causes lamp 1 to turn off and the resulting low intensity of the incident light on photocell 11 makes its resistance sharply rise. Transistor 13 is thereby biased so as to normally be nonconductive. However, it is held in the fully conductive condition for a selected interval because of the capacitive discharge current flowing through photocell 11 and resistor 23. The discharge current maintains the voltage at terminal 25 of base bias resistor 15 sufliciently low to maintain transistor 13 fully conductive for an interval determined by the time constant of that discharge path. At the end of that interval the voltage at terminal 25 will have exponentially risen to a level determined by the resistance of resistor 15 at which transistor 13 begins to become less conductive. This enables transistor 9 to begin to conduct, so that another entire flashing cycle is initiated as described.

From the above it will be clear that when lamp 1 has been turned off it will remain so for a period dependent on the charging time of capacitor 21 in the path comprising resistor 23 and photocell 11. Since the photocell resistance will then be high this period will tend to be relatively long. On the other hand, when lamp 1 is turned on it will remain so for a period dependent on the discharge time of capacitor 21 in the foregoing path. As the photocell resistance is then low the on period will normally be relatively short. Increasing the capacitance of capacitor 21 or the resistance of resistor 23 will lengthen both of the foregoing periods and so will reduce the flashing frequency. The relative durations of successive on and oil periods can be controlled by adjustment of the resistance of base bias resistor 15 of transistor 13. Increasing the resistance thereof will increase the amount by which the voltage at its terminal 25 must fall in order to enable transistor 13 to conduct after lamp 1 turns on. Thus the on period of the lamp will be increased. At the same time, increasing the resistance of resistor 15 will reduce the degree of forward bias of transistor 13 when it becomes fully conductive and lamp 1 turns off. The amount by which the voltage at terminal 25 must rise in order to cause transistor 13 to begin to become less conductive will therefore be reduced and the off period of lamp 1 will be shortened. Reducing the resistance of resistor 15 will have just the opposite effect in each case, resulting in a decrease in the on period and an increase in the 05 period of lamp ll. Of course, this resistance must always be in a range wherein it is low enough so transistor 13 dri 'es transistor 9 to cutofi when the light on photocell 11 reaches the selected high intensity and wherein it is high enough so transistor 13 drives transistor 9 fully conductive when the incident light reaches a low threshold level such as normally encountered at nighttime in the vicinity of the device.

Typical values of the various circuit components for operation at a dashing frequency of sixty (60) flashes per minute and wherein lamp 1 is on for ten percent of the period of each cycle and off for ninety percent (9G%) thereof are as follows:

Capacitor 19 3.0 mfd.

Resistor l5 100 kilohrns.

Resistor l7 5.6 kilohms.

Resistor 23 3.3 kilohms.

Photocell Clairex cadmium sulfide Type GL4.

Lamp General Electric No. 1850;

90 milliamperes.

Battery 6 volts.

The selected light intensity at which lamp 1 is maintained off will depend on the resistance of resistor 15, a larger value thereof requiring a higher light intensity in order to keep transistor 9 nonconductive. However, since the ambient light intensity at daybreak changes very sharply, the resistance can actually lie anywhere within a very wide range without appreciable effect on the total time during which lamp 1 is kept ofl during each day. This resistance can thus still be selected so to attain a desired on-ofl" flash ratio as described above.

While the invention has been described with reference to a particular preferred embodiment thereof it will be apparent to those skilled in the art that it is susceptible to many modifications and variations without departing rom the true teachings and scope of the invention as defined by the ensuing claims.

What is clairned is:

1. A flashing light device comprising: a direct current supply circuit; a lamp; a transistor connected in series with said lamp in said supply circuit so as to cause the lamp to turn on at full intensity when said transistor is fully conductive and cause the lamp to turn on when said transistor is nonconductive; photosensitive means disposed in proximity to said lamp so as to be subjected to the light therefrom as well as to the ambient light in the vicinity of said device, said photosensitive means having an electrical characteristic which varies in accordance with variations in the intensity of the light incident thereon; control means including a second transistor connected to said supply circuit by said photosenstiive means and responsive to variation of said electrical characteristic thereof to produce a control voltage which ranges between a limiting level and a cutoff level in accordance with variation of the incident light between respectively corresponding threshold and selected high intensities, said selected high intensity being at most equal to the full intensity of said lamp; direct conductor means for connecting said second transistor as said control means to said transistor so as to form a degenerative feedback loop wherein said control voltage causes said transistor to conduct to a degree ranging from fully conductive to nonconductive in correspondence with variation of said control voltage between its limiting and cutofi levels; and means for further connecting said control means to said transistor in a regenerative feedback loop which renders said transistor fully conductive for a controlled interval whenever said control voltage changes from the cutoff level toward the limiting level and which renders it fully nonconductive for a controlled interval whenever said control voltage changes from the limiting level toward the cutoff level; whereby said lamp is caused to cyclically flash fully on and off so long as the ambient light remains below said selected high intensity and is maintained off when the ambient light is at least a. that intensity.

2. A flashing light device comprising: a direct current supply circuit; a lamp; a transistor connected in series with said lamp in said supply circuit so as to cause the lamp to turn on at full intensity when said transistor is fully conductive and cause the lamp to turn off when said transistor is nonconductive; a photocell disposed in proximity to said lamp so as to be subjected to the light therefrom as well as to the ambient light in the vicinity of said device, said photocell having an electrical resistance which decreases as the intensity of the light incident thereon increases; control means including a second transistor connected to said supply circuit by said photocell and responsive to the resistance variation thereof to produce a control voltage which ranges between a limiting level and a cutoff level in accordance with variation of the incident light between respectively corresponding threshold and selected high intensities, said selected high intensity being at most equal to the full intensity of said lamp; direct conductor means for connecting said second transistor of said control means to said transistor so as to form a degenerative feedback loop wherein said control voltage causes said transistor to conduct to a degree ranging from fully conductive to nonconductive in correspondence with variation of said control voltage between its limiting and cutoff levels; and means for further connecting said control means to said transistor in a regenerative feedback loop which renders said transistor fully conductive for a controlled interval whenever said control voltage changes from the cutolf level toward the limiting level and which renders it fully nonconductive for a controlled interval whenever said control voltage changes from the limiting level toward the cutofi level; whereby said lamp is caused to cyclically fiash fully on and off so long as the ambient light remains below said selected high intensity and is maintained off when the ambient light is at least at that intensity.

3. A flashing light device comprising: a direct current supply circuit; a lamp; a first transistor connected in series With said lamp in said supply circuit so as to cause the lamp to turn on at full intensity when said first transistor is fully conductive and cause the lamp to turn off when said first transistor is nonconductive; a photocell disposed in proximity to said lamp so as to be subjected to the light therefrom as Well as to the ambient light in the vicinity of said device, said photocell having an electrical resistance which decreases as the intensity of the light incident thereon increases; control means including a second transistor connected to said supply circuit by said photocell and responsive to the resistance variation thereof to produce a control voltage which ranges between a limiting level and a cutoff level in accordance with variation of the incident light between respectively corresponding threshold and selected high intensities, said selected high intensity being at most equal to the full intensity of said lamp; direct conductor means for connecting said second transistor to said first transistor so as to form a degenerative feedback loop wherein said control voltage causes said first transistor to conduct to a degree ranging from fully conductive to nonconductive in correspondence with variation of said control voltage between its limiting and cutofi levels; and means for further connecting said second transistor to said first transistor in a regenerative feedback loop which renders said first transistor fully conductive for a controlled interval whenever said control voltage changes from the cutoif level toward the limiting level and which renders it fully nonconductive for a controlled interval whenever said control voltage changes from the limiting level toward the cutoff level; whereby said lamp is caused to cyclically flash fully on and oif so long as the ambient light remains below said selected high intensity and is maintained oft when the ambient light is at least at that intensity.

4. A flashing light device comprising: a direct current supply circuit; a lamp; a first transistor connected in series with said lamp in said supply circuit so as to cause the lamp to turn on at full intensity when said transistor is fully conductive and cause the lamp to turn ofi when said transistor is nonconductive; a photocell disposed in proximity to said lamp so as to be subjected tothe light therefrom as well as to the ambient light in the vicinity of said device, said photocell having an electrical resistance which decreases as the intensity of the light incident thereon increases; control means including a second transistor connected to said supply circuit by said photocell and responsive to the resistance variation thereof to become biased to a degree ranging between the nonconductive state and the fully conductive state in accordance with variation of the incident light between respectively corresponding threshold and selected high intensities, said selected high intensity being at most equal to the full intensity of said lamp; direct conductor means for connecting said second transistor to said first transistor so as to apply a bias voltage to the first transistor which causes it to conduct to a degree ranging from fully conductive whenthe second transistor is in the nonconductive state to fully nonconductive when the second transistor is in the fully conductive state; and means for further connecting said second transistor to said first transistor in a regenerative feedback loop which renders said first transistor fully conductive for a controlled interval whenever said second transistor begins to change from the nonconductive toward the fully conductive state and which renders said first transistor nonconductive for a controlled interval whenever said second transistor begins to change from the fully conductive toward the nonconductive state; whereby said lamp is caused to cyclically flash fully on and off so long as the ambient light remains below said 8' selected high intensity and is maintained oil when the ambient light is at least at that intensity.

5. A flashing light device comprising: a direct current supply circuit; a lamp; a first transistor connected in series with said lamp in said supply circuit so as to cause the lamp to turn on at full intensity when said transistor is fully conductive and cause the lamp to turn off when said transistor is nonconductive; a photocell disposed in proximity to said lamp so as to be subjected to the light therefrom as well as to the ambient light in the vicinity of said device, said photocell having an electrical resistance which decreases as the intensity of the light incident thereon increases; control means including a second transistor connected to said supply circuit by said photocell and responsive to the resistance variation thereof to become biased to a degree ran ing between the nonconductive state and the fully conductive state in accordance with variation of the incident light bet veen respectively corresponding threshold and selected high intensities, said selected high intensity being at most equal to the full intensity of said lamp; means for directly connecting said second transistor to said first transistor so as to apply a bias voltage to the first transistor which causes it to conduct to a degree ranging from fully conductive when the second transistor is in the nonconductive state to fully nonconductive when the second transistor is in the fully conductive state; and a capacitive coupling between said second transistor and said first transistor for establishing a regenerative feedback loop which renders said first transistor fully conductive for a controlled interval whenever said second transistor begins to change from the nonconductive toward the fully conductive state and which renders said first transistor non-conductive for a controlled interval whenever said second transistor begins to change from the fully conductive toward the nonconductive state; whereby said lamp is caused to cyclically flash fully on and oif so long as the ambient light remains below said selected high intensity and is maintained off when the ambient light is at least at that intensity.

6. A flashing light device comprising: a direct current supply circuit; a lamp; a first transistor having its emitter and collector in series with said lamp in said supply circuit so as to cause the lamp to turn on at full intensity when said first transistor is fully conductive and cause the lamp to turn ofi when said first transistor is nonconductive; a photocell disposed in proximity to said lamp so as to be subjected to the light therefrom as well as to the ambient light in the vicinity of said device, said photocell having an electrical resistance which decreases as the intensity of the light incident thereon increases; a second transistor connected at its emitter to the emitter of said first transistor; a first resistor for connecting the collector of said second transistor to said supply circuit; a second resistor connected in series with said photocell between said supply circuit and the base of said second transistor so as to bias that transistor to a degree responsive to the resistance variation of said photocell and ranging between the nonconductive state and the fully conductive state in accordance with variation of the incident light between respectively corresponding threshold and selected high intensities, said selected high intensity being at most equal to the full intensity of said lamp; means for connecting the collector of said second transistor to the base of said first transistor so as to apply a bias voltage to said base which causes said first transistor to conduct to a degree ranging from fully conductive when said second transistor is in the nonconductive state to fully nonconductive when the second transistor is in the fully conductive state; a capacitive coupling between the base of said second transistor and the collector of said first transistor for establishing a regenerative feedback loop which renders said first transistor fully conductive for a controlled interval whenever said second transistor begins to change from the nonconductive toward the fully conductive state and which renders said 9 first transistor nonconductive for a controlled interval whenever said second transistor begins to change from the fully conductive toward the nonconductive state, the total of successive conductive and nonconductive intervals of said first transistor being determined by the time constant of said capacitive coupling and the relative durations thereof being determined by the esistance of said first resistor; whereby said lamp is caused to cyclically flash References Cited in the file of this patent UNITED STATES PATENTS Coleman Aug. 25, 1959 Pederson Dec. 8, 1959 

1. A FLASHING LIGHT DEVICE COMPRISING: A DIRECT CURRENT SUPPLY CIRCUIT; A LAMP; A TRANSISTOR CONNECTED IN SERIES WITH SAID LAMP IN SAID SUPPLY CIRCUIT SO AS TO CAUSE THE LAMP TO TURN ON AT FULL INTENSITY WHEN SAID TRANSISTOR IS FULLY CONDUCTIVE AND CAUSE THE LAMP TO TURN OFF WHEN SAID TRANSISTOR IS NONCONDUCTIVE; PHOTOSENSITIVE MEANS DISPOSED IN PROXIMITY TO SAID LAMP SO AS TO BE SUBJECTED TO THE LIGHT THEREFROM AS WELL AS TO THE AMBIENT LIGHT IN THE VICINITY OF SAID DEVICE, SAID PHOTOSENSITIVE MEANS HAVING AN ELECTRICAL CHARACTERISTIC WHICH VARIES IN ACCORDANCE WITH VARIATIONS IN THE INTENSITY OF THE LIGHT INCIDENT THEREON; CONTROL MEANS INCLUDING A SECOND TRANSISTOR CONNECTED TO SAID SUPPLY CIRCUIT BY SAID PHOTOSENSITIVE MEANS AND RESPONSIVE TO VARIATION OF SAID ELECTRICAL CHARACTERISTIC THEREOF TO PRODUCE A CONTROL VOLTAGE WHICH RANGES BETWEEN A LIMITING LEVEL AND A CUTOFF LEVEL IN ACCORDANCE WITH VARIATION OF THE INCIDENT LIGHT BETWEEN RESPECTIVELY CORRESPONDING THRESHOLD AND SELECTED HIGH INTENSITIES, SAID SELECTED HIGH INTENSITY BEING AT MOST EQUAL TO THE FULL INTENSITY OF SAID LAMP; DIRECT CONDUCTOR MEANS FOR CONNECTING SAID SECOND TRANSISTOR AS SAID CONTROL MEANS TO SAID TRANSISTOR SO AS TO FORM A DEGENERATIVE FEEDBACK LOOP WHEREIN SAID CONTROL VOLTAGE CAUSES SAID TRANSISTOR TO CONDUCT TO A DEGREE RANGING FROM FULLY CONDUCTIVE TO NONCONDUCTIVE IN CORRESPONDENCE WITH VARIATION OF SAID CONTROL VOLTAGE BETWEEN ITS LIMITING AND CUTOFF LEVELS; AND MEANS FOR FURTHER CONNECTING SAID CONTROL MEANS TO SAID TRANSISTOR IN A REGENERATIVE FEEDBACK LOOP WHICH RENDERS SAID TRANSISTOR FULLY CONDUCTIVE FOR A CONTROLLED INTERVAL WHENEVER SAID CONTROL VOLTAGE CHANGES FROM THE CUTOFF LEVEL TOWARD THE LIMITING LEVEL AND WHICH RENDERS IT FULLY NONCONDUCTIVE FOR A CONTROLLED INTERVAL WHENEVER SAID CONTROL VOLTAGE CHANGES FROM THE LIMITING LEVEL TOWARD THE CUTOFF LEVEL; WHEREBY SAID LAMP IS CAUSED TO CYCLICALLY FLASH FULLY ON AND OFF SO LONG AS THE AMBIENT LIGHT REMAINS BELOW SAID SELECTED HIGH INTENSITY AND IS MAINTAINED OFF WHEN THE AMBIENT LIGHT IS AT LEAST AT THAT INTENSITY. 